I weighted a 20x11 for a 2012 Mercedes CLS63 at 22.4 lbs.
For the Z, which has a very low offset, you will tend to see higher weights. I would estimate 19x10.5 with low offset will be in the 22 lb range. With a lot of the newer vehicles, car manufacturers have moved to high offset, which makes the wheels lighter. Z/GTR is not one of those cars
That's why you can get those really conical profiles on the Z/GTR.